1. Technical Field
The present invention relates to a projector and a method for controlling the projector.
2. Related Art
Conventionally, a projector includes an exhaust fan for exhausting air in an enclosure of the projector. The reason for this is that an increase in temperature in the enclosure due to use of a high-intensity lamp lowers the performance of optical parts that form a liquid crystal panel, a polarization conversion system, a color separation/light combining system, and other optical systems. For example, JP-A-2003-5289 discloses a projector that includes an exhaust fan and an intake fan and controls the rotational speeds of the exhaust fan and the intake fan in accordance with the temperature of sucked outside air detected with a temperature sensor.
In recent years, power consumption of projectors has been continuously reduced. To this end, a projector having what is called a power saving mode is provided. In the power saving mode, electric power supplied to a lamp when no image is displayed is reduced to about 20% to 30% of rated power. When the projector is operated in the power saving mode, the luminance of the lamp decreases and the temperature of the lamp becomes lower than that in normal operation. The lamp is therefore overcooled in some cases if a cooling fan is driven at the same number of revolutions as that in the normal operation. In this case, vapor in the lamp condenses, resulting in a problem of a decrease in reliability of the lamp.
To avoid the problem, it is preferable to sufficiently lower the number of revolutions of the cooling fan when the projector is operated in the power saving mode. The reason for this is that completely stopping the cooling fan is not preferable because the temperatures of a variety of optical parts increase and performance and reliability thereof may not be ensured. In general, however, the specifications of a cooling fan are determined based on cooling capability at high temperatures (usable limit of cooling fan running at high rotational speed). When a designer of the projector determines the specifications of the cooling fan in consideration of the cooling capability at high temperatures, a usable limit of the cooling fan running at a low rotational speed is determined automatically. The designer is therefore not free to set the specifications of the cooling fan running at a low rotational speed. It is therefore difficult for the designer to set the number of revolutions of the cooling fan running at a low rotational speed in such a way that both the reliability of the lamp or any other light source section and the performance and reliability of a variety of optical parts are ensured.